1. Field of the Invention
The present invention relates to a power transmission device, especially to a transmission device used in an automatic document feeder.
2. The Related Art
Referring to FIG. 1, it shows a schematic diagram of a conventional automatic document feeder. The automatic document feeder defines a paper transmitting path that is consisted of an input tray 14, an input path 13, a scanning area 17, an output path 15, and an output tray 16 in sequence from upstream to downstream. A reverse path 18 is connected between the input path 13 and the output path 15.
In order to convey documents through the paper transmitting path, a plurality of transmission devices are placed along the paper transmitting path. For example, a pickup device 10 is provided at the inlet end of the input path 13, a plurality of transmitting rollers 11 are provided along the input path 13 and the output path 15, and an output device 12 is provided at the outlet end of the output path 15.
When the documents need to be scanned by the automatic document feeder, the pickup device 10 will descend for transmitting one of the documents into the input path 13. After the document enters the input path 13 and reaches the transmitting roller 11, the pickup device 10 will rise to avoid multiple feeding.
Next, the transmitting rollers 11 disposed along the input path 13 and the output path 15 rotate to transmit the document into the scanning area 17 for being scanned, and further transmit the scanned document to the output tray 16.
The output device 12 placed at the outlet end of the output path 15 is provided with a driving roller 121 and a movable idle roller 123. The idle roller 123 keeps contact with the driving roller 121 to apply normal force to the documents in the process of single-side scanning. But in the process of double-side scanning, the output device 12 will reverse and transmit the document finished its first-side scanning into the reverse path 18. Then the document passes through the reverse path 18 to return into the input path 13 and face a scanning device of the scanning area 17 with the second side thereof. In order to avoid document jam by the output device 12 in the process of double-side scanning, the idle roller 123 will swing down to separate from the driving roller 121.
It is known that the pickup device 10, the transmitting rollers 11 and the output device 12 have great difference about their actuation timing and rotation direction. The transmitting rollers 11 basically keeps rotating in the same direction, the pickup device 10 and the output device 12 will change their rotate directions according to the location of the documents, and the driving rollers 121 and the idle roller 123 of the output device 12 will need to separate from each other in the process of double-side scanning. Therefore, most of conventional automatic document feeders would use at least two motors or a clutch with a solenoid to operate the pickup device 10, the transmitting rollers 11 and the output device 12 respectively. As a result, the conventional automatic document feeder has higher manufacture cost and is harder to be miniaturized.
To solve the above disadvantages, the transmission device used in the conventional automatic document feeder is necessary to be improved.